1. Field of the Invention
This invention relates to a method for producing chain internal and/or end positioned vicinal alkylene glycols having from 6 to 24 carbon atoms by hydrolyzing a corresponding epoxyalkane at elevated temperature and pressure.
2. Brief Description of the Background of the Invention Including Prior Art
According to older known processes, alkylene oxides are heated in the presence of a catalyst with a large excess of water. The excess of water prevents in fact the undesired formation of di-, tri- and polyalkyleneglycols, but results in the disadvantage that only alkyleneglycol solutions of low concentration are obtained. For the technical preparation of vicinal glycols these proceses are less suitable, since the work up of the low concentration glycol solutions requires a lot of energy and a high expenditure for equipment. In addition, the yields amount to only about 90 percent of theory even with comparably long reaction times.
More recent processes are also known providing without or with small water excess yields of about 97 percent.
According to a process disclosed in German Offenlegungsschrift DE-OS 17 93 247, which corresponds to U.S. Pat. No. 3,629,343, alkylene oxides, especially ethylene oxide and propylene oxide, are hydrolyzed in the presence of carbon dioxide under a pressure of from 10 to 180 bar and at a temperature from 80.degree. to 220.degree. C. in the presence of an alkali metal halogenide or of a quaternary ammonium compound as a catalyst. The alkylene oxide, water and carbon dioxide form initially an alkylene carbonate, which then with water forms the desired vicinal glycol after splitting off of carbon dioxide. Preferably, this hydrolysis is performed in the presence of basic compounds, for example carbonates, bicarbonates or alkali metal hydroxides, in order to decrease the formation of dialkylene glycols and to accelerate the process.
Disadvantages of the process include comparatively long reaction times and the fact that the required catalyst cannot be completely separated from the reaction product. The content of halides present in the glycols is so large that they are unsuitable for certain applications. In addition, this known process shows no advantage when higher, water-insoluble epoxides are employed regarding the yield, since the reaction is performed in heterogeneous phases. Accordingly, a continuous reaction of higher alkylene oxides cannot be considered herein.
A process improved specifically with regard to the preparation of ethylene glycol is described in the German Offenlegungsschrift DE-OS 21 41 470. Instead of the halogen compounds, the catalysts used are alkali salts of aliphatic, alicyclic or one or more ring aromatic mono- or dicarboxylic acids as well as aliphatic or aromatic hydroxycarboxylic acids.
From the German Offenlegungsschriften DE-OS 21 09 453 and 22 03 806 a process is known for the preparation of chain internal, end positioned or cyclical vicinal glycols with from 8 to 30 carbon atoms. The water insoluble epoxides are split in the presence of alkaline acting compounds with strong agitation at temperatures of from 150.degree. C. to 300.degree. C. under the pressures thereby produced (about 30 to 60 bar). Alkali hydroxides are herein employed as alkaline acting compounds. It is a disadvantage of this process that the reaction occurs between heterogeneous phases and that intense mixing of the reaction mixture is required. Since in addition, reaction times of from half an hour to two hours are required, this process is not suitable for the technical continuous production of higher vicinal glycols.
Furthermore, the German Offenlegungsschrift DE-OS 22 56 907 discloses a process for the production of vicinal glycols wherein the hydrolysis is performed with aqueous solutions of salts of aliphatic mono- and/or polycarboxylic acids at temperatures above 100.degree. C. and preferably from 200.degree. C. to 300.degree. C. and if desired in the presence of a solubilizer. The hydrolysis is performed in 1 to 20 percent and preferably 2 to 5 weight percent salt solutions. The solubilizer, which is preferably a water soluble ketone or a cyclical ether such as acetone, dioxane and/or dioxolane is employed in an amount of from 0.5 to 2 parts by weight per weight part of epoxide. In fact this process provides in part fairly good yields and short reaction times, however also in this process the reaction mixture has to be agitated. It is another disadvantage of this process that comparatively expensive auxiliary materials are required.